Various objects such as semiconductor wafers, masks, printed circuit boards, solar panels, microelectromechanical devices, are manufactured by manufacturing processes that are highly complex and costly, comprise multiple stages, and require highly accurate machines. Such objects are generally referred to as wafers.
The complex manufacturing process is not error free and such errors can cause faults or alleged faults in the manufactured objects. The faults can include defects that can harm the operation of the object, false positive findings, which may seem to contain a defect although there is no actual defect at the area, and nuisances which may be defects but do not cause any harm or malfunction of the manufactured unit. In addition to faults in the raw material, human errors and others may also cause defects in the objects.
The term “defect” used in this specification should be expansively construed to cover any kind of abnormality or undesirable feature formed on or within a wafer.
The term “examination”, unless specifically stated otherwise, used in this specification in a relation to a wafer should be expansively construed to cover any kind of detection and/or classification of defects in the wafer provided by using non-destructive inspection tools. By way of non-limiting example, such examination can include generating one or more recipes for examination and/or parts thereof; inspection, e.g., scanning in a single or in multiple scans; reviewing; measuring and/or other operations provided with regard to the wafer or parts thereof using the same or different inspection tools.
In order to find defects, various examination steps can be integrated into the manufacturing process, including inspection and review. The examination steps can be performed a multiplicity of times, for example at certain stages such as after the manufacturing or processing of certain layers, or the like. Additionally or alternatively, each examination step can be repeated multiple times, for example for different wafer locations or for the same wafer locations with different examination settings.
By way of non-limiting example, examination can employ a two phase “inspection and review” procedure.
The term “inspection” refers to scanning and analyzing a wafer or a part thereof, in order to detect locations in which defects may be found. Suspicious locations reported by an inspection can include true defects, false positive reports, and nuisance defects, which are harmless. A variety of non-destructive inspection tools can be used, which include, by way of non-limiting example, scanning electron microscopes, atomic force microscopes, optical inspection tools, etc.
The term “review” refers to capturing and analyzing one or more specific locations, for example locations of potential defects reported by the inspection process, locations of interest derived from design data, locations indicated by a user, or the like.
The term “design data” used in the specification should be expansively construed to cover any data indicative of hierarchical physical design (layout) of a specimen. Design data can be provided by a respective designer and/or can be derived from the physical design (e.g. through complex simulation, simple geometric and Boolean operations, etc.). Design data can be provided in different formats as, by way of non-limiting examples, GDSII format, OASIS format, etc. Design data can be presented in vector format, grayscale intensity image format or otherwise. Design data comprise design structural elements that represent different features to be formed on one or more layers of a specimen. As known in the contemporary art, a design structural element can be constructed as a geometrical shape with a closed contour or a geometrical shape combined with insertion of other structural elements. By way of non-limiting examples, a given design structural element can comprise one or more STRUCTURE elements inserted by means of SREF, AREF directives in GDSII format, or can comprise one or more CELL elements inserted by means of PLACEMENT and REPETITION (OASIS format).
Typically, inspection is performed at higher speed and lower resolution than review. Thus, inspection can be used for covering larger areas and detecting potential defects, wherein some or all of which can later be reviewed and optionally further examined. During review, some of the potential defects reported by the inspection tool can prove to be false alarms.
In some embodiments, inspection and review can be performed by different tools, but in other embodiments they can be performed by the same tool.
General Description
One aspect of the disclosure relates to a method for examining an object using a processor operatively connected to a memory, the method comprising: receiving a multiplicity of potential defects, each potential defect of the multiplicity of potential defects associated with a potential defect location; performing a first clustering of the multiplicity of potential defects to obtain a first subset and one or more second subsets, the clustering performed in accordance with spatial distances between potential defect locations, such that potential defects in the first subset are characterized by higher density in one or more physical areas than potential defects comprised in the second subsets; automatically assigning first probabilities to be valid defects to potential defects in the first subset, the first probabilities calculated in accordance with a first policy; automatically assigning second probabilities to be valid defects to potential defects in the second subsets, the second probabilities calculated in accordance with a second policy specifying how to combine two or more second factors; automatically selecting and assigning for review by a review tool a potential defect from the first subset and the second subsets, in accordance with a third policy specifying how to combine potential defects from a multiplicity of subsets into a merged list, and in accordance with a strategy indicating how to combine top elements from the merged list and randomly selected elements from the merged list, in accordance with considerations including number of reviews; receiving validity or class indications for potential defects in the part of the potential defect lists, the indications received subsequent to potential defects in the part of the potential defect lists being reviewed by the review tool; and subsequent to a stopping criteria not being observed: updating the first, second, or third policy in accordance with validation or classification of an item in the first subset and the second subsets; and repeating said assigning, selecting, receiving and updating, in accordance with the first, second, or third policy as updated, until the stopping criteria is observed. Within the method, the stopping criteria is optionally selected from the group consisting of: a predetermined number of potential defects have been reviewed by the review tool; convergence of a number of indications that a potential defect is valid; and a predetermined number of defects associated with a specific defect class have been detected. Within the method, a decision confidence level is optionally received for the validity or class indications received. Within the method, a physical area is optionally selected from the group consisting of: a region; an area in the vicinity of an open line; and an area in the vicinity of a close line. The method can further comprise performing a second clustering of the second subset based on characteristics other than geometric location. Within the method, the characteristics of the second clustering optionally include an item selected from the group consisting of: shade or color of the wafer at a location of a potential defect; background shade or color of the wafer at an area of the potential defect; edges in the vicinity of the potential defect; a feature in the vicinity of the potential defect; number of polygons, edges, or corners and density thereof in the vicinity of the potential defect. Within the method, the second clustering optionally provides for determining potential defects located in a dense area in relation to characteristics used for the second clustering, thereby providing for determining systematic potential defects. Within the method, the two or more second factors in respect of the random potential defects are optionally selected from the group consisting of: being located at an area which is sparse in feature space in relation to the characteristics used for the second clustering; being located at an outlier area of an area which is dense in feature space in relation to the characteristics used for the second clustering; proximity to a validated potential defect; and a combination of two or more of the above, thereby providing for determining random potential defects. Within the method, the random potential defects are optionally associated with two or more scans taken by different tools or under different conditions. Within the method, automatically selecting and assigning for review optionally comprises: sorting potential defects of the first subset according to the first probability, to obtain a first sorted list; sorting each of the second subsets according to the second probability, to obtain one or more second sorted lists; prioritizing potential defects from the first sorted list or the second sorted lists to form a merged list, in accordance with the third policy; and selecting potential defects to be reviewed from the merged list in accordance with the strategy. Within the method, the third policy optionally complies with one or more items selected from the group consisting of: selecting a predetermined percentage of a required number of potential defects from the first sorted list and complementing with potential defects from the second sorted lists; selecting top probability potential defects from a merged list of the first sorted list and the second sorted lists, sorted by probability; and prioritizing potential defects from the first sorted list or the second sorted lists in accordance with user input and selecting top priority potential defects. Within the method, the strategy optionally indicates a number of top probability potential defects to be selected from the merged list, and complementing with randomly selected potential defects from the merged list. Within the method, the strategy optionally changes between iterations. Within the method, the strategy optionally changes between iterations in accordance with an item selected from the group consisting of: increasing the number of randomly selected potential defects in advanced iterations relative to earlier iterations; increasing the number of randomly selected potential defects if a number of true defects identified in a previous iteration is below a threshold; increasing the number of randomly selected potential defects if a number of true defects identified in a previous iterations converges; and changing the number of randomly selected potential defects in accordance with type or location distribution of true defects identified in one or more previous iterations. Within the method, assigning the first probabilities or assigning the second probabilities optionally comprises receiving a user indication to assign higher priority to potential defects at specific areas or of specific classes. Within the method, the object is optionally a wafer or a mask.
Another aspect of the disclosure relates to a computerized system comprising a processor configured for: receiving a multiplicity of potential defects, each potential defect of the multiplicity of potential defects associated with a potential defect location; performing a first clustering of the multiplicity of potential defects to obtain a first subset and one or more second subsets, the clustering performed in accordance with spatial distances between potential defect locations, such that potential defects in the first subset are characterized by higher density in a physical area than potential defects comprised in the second subsets; automatically assigning first probabilities to be valid defects to potential defects in the first subset, the first probabilities calculated in accordance with a first policy; automatically assigning second probabilities to be valid defects to potential defects in the second subsets, the second probabilities calculated in accordance with a second policy specifying how to combine two or more second factors; automatically selecting and assigning for review by a review tool one or more potential defects from the first subset and the second subsets, in accordance with a third policy specifying how to combine potential defects from a multiplicity of subsets into a merged list, and in accordance with a strategy indicating how to combine top elements from the merged list and randomly selected elements from the merged list, in accordance with considerations including number of reviews; receiving validity or class indications for potential defects in a part of the potential defect lists, the indications received subsequent to potential defects in the part of the potential defect lists being reviewed by the review tool; and subsequent to a stopping criteria not being observed: updating the first, second, or third policy in accordance with validation or classification of an item in the first subset and the one second subsets; and repeating said assigning, selecting, receiving and updating, in accordance with the first, second, or third policy as updated, until the stopping criteria is observed. Within the system, the stopping criteria is optionally selected from the group consisting of: a predetermined number of potential defects have been reviewed by the review tool; convergence of a number of indications that a potential defect is valid; and a predetermined number of defects associated with a specific defect class have been detected. Within the system, automatically selecting and assigning for review comprises: sorting potential defects of the first subset according to the first probability, to obtain a first sorted list; sorting each of the second subsets according to the second probabilities, to obtain second sorted lists; prioritizing potential defects from the first sorted list or the second sorted lists to form a merged list, in accordance with the third policy; and selecting potential defects to be reviewed from the merged list in accordance with the strategy, and wherein the third policy complies with an item selected from the group consisting of: selecting a predetermined percentage of a required number of potential defects from the first sorted list and complementing with potential defects from the second sorted lists; selecting top probability potential defects from a merged list of the first sorted list and the second sorted lists, sorted by probability; and prioritizing potential defects from the first sorted list or the second sorted lists in accordance with user input and selecting top priority potential defects.
Yet another aspect of the disclosure relates to a computer program product comprising a computer readable storage medium retaining program instructions, which program instructions when read by a processor, cause the processor to perform a method comprising: receiving a multiplicity of potential defects, each potential defect of the multiplicity of potential defects associated with a potential defect location; performing a first clustering of the multiplicity of potential defects to obtain a first subset and one or more second subsets, the clustering performed in accordance with spatial distances between potential defect locations, such that potential defects in the first subset are characterized by higher density in a physical area than potential defects comprised in the second subsets; automatically assigning first probabilities to be valid defects to potential defects in the first subset, the first probabilities calculated in accordance with a first policy; automatically assigning second probabilities to be valid defects to potential defects in the second subsets, the second probabilities calculated in accordance with a second policy specifying how to combine two or more second factors; automatically selecting and assigning for review by a review tool one or more potential defects from the first subset and the second subsets, in accordance with a third policy specifying how to combine potential defects from a multiplicity of subsets into a merged list, and in accordance with a strategy indicating how to combine top elements from the merged list and randomly selected elements from the merged list, in accordance with considerations including number of reviews; receiving validity or class indications for potential defects in a part of the potential defect lists, the indications received subsequent to potential defects in the part of the potential defect lists being reviewed by the review tool; and subsequent to a stopping criteria not being observed: updating the first, second, or third policy in accordance with validation or classification of an item in the first subset and the second subsets; and repeating said assigning, selecting, receiving and updating, in accordance with the first, second, or third policy as updated, until the stopping criteria is observed.